This paper presents a parametric, experimental study of the performance of gas and liquid propane injection in a spark ignition, multi-point port injected (MPI) engine. An inline, six cylinder engine is used over a wide range of speeds and torques, and the air/fuel ratio, compression ratio and injection timing are all varied. The engine was mapped at the standard compression ratio of 9.65:1 with the original, gasoline MPI system, propane gas MPI, and single point, throttle body, propane gas injection. Gas and liquid propane MPI are then tested at a compression ratio of 11.7:1.
Contour plots of thermodynamic efficiency and the specific emissions of HC, NOx, CO2 and CO over the torque/speed range are presented and compared. The results show significant differences in performance between gas and liquid propane MPI injection, as well as the MPI and throttle body gas injection. Previous research has in part attributed this difference in performance to the increased volumetric efficiency of the liquid propane injection. This paper examines gas and liquid injection of propane and proposes that the difference in the method of mixing also significantly affects engine performance. Significant improvements in emissions and thermal efficiencies were achieved when compared with gasoline, eg. specific emissions reductions of 88% for HC, 45% for NOx, 40% for CO2, 92% for CO and a rise of 27% in thermal efficiency.